The present invention relates to ink jet heads for non-impact printers, in which ink is jet from a nozzle for printing.
With recent office automation development, various printers are finding various applications. These printers are in dependence on the type of printing classified into impact printers for impact printing and non-impact printers for non-impact printing. The non-impact printers are capable of low noise, high resolution and relatively high speed printing. These printers include ink jet printers and are finding extensive applications.
A prior art ink jet printer adopts an ink jet head as shown in FIG. 5, for instance. Referring to the Figure, the illustrated ink jet head 51 comprises a laminate piezoelectric element 52 and a circuit substrate 53.
The laminate piezoelectric element 52 has inner and outer electrodes 54 and 55 in conductive connection with one another. Oscillations of the laminate piezoelectric element 52 are transmitted via an adhesive layer 58 and an oscillating plate 59 to a pressure chamber 57 communicated with an ink jet nozzle 56. The pressure chamber 57 is formed by the oscillating plate 59 and a nozzle plate 60.
The circuit substrate 53 is connected to the laminate piezoelectric element 52 via a flexible printed circuit board or lead members 61 such as wires. The circuit substrate 53 is formed with a driver IC (not shown) for driving the laminate piezoelectric element 52, and connectors 62 for connecting the laminate piezoelectric element 52 are mounted on the circuit substrate 53.
A drive signal is thus supplied from the driver IC (not shown) of the circuit substrate 53 to the laminate piezoelectric element 52. The circuit substrate 53 is formed with a conductive pattern (not shown), which connects the connectors 60 and the drive IC (not shown) to one another.
With the ink jet head having the above construction, a drive signal supplied from the circuit substrate 53 to the laminate piezoelectric element 52 generates oscillations thereof, and the oscillations thus generated are transmitted via the adhesive layer 58 and the oscillating plate 59 to the pressure chamber 57 to cause jetting of ink from the nozzle 56.
However, this prior art ink jet head uses the lead members 61 for connecting the laminate piezoelectric element 52 and the circuit substrate 53 to each other. Noise that is introduced increases the possibility of erroneous head operation, thus deteriorating the qualitative reliability.
Particularly, in a multiple nozzle structure having a large number of laminate piezoelectric elements 52 connected to the circuit substrate 53, the erroneous head operation possibility due to noise introduction is increased by an increased number of lead members 61.
In another aspect, each laminate piezoelectric element 52 and the circuit substrate 53 should be spaced apart by a certain distance. This distance causes the characteristic impedance increase and the induced voltage applied increase to the drive IC. The induced voltage increase does not only result in inter-drive signal crosstalk increase, waveform dulling and ringing to cause erroneous head operation, but also result in the destroy or routine of the drive IC.
Furthermore, the increase of the number of the lead members 61 increases the number of times of connection of the lead members 61. Therefore, the operability of connection of the laminate piezoelectric elements 52 to the circuit substrate 53 is correspondingly deteriorated to reduce the yield.
Still further, since the lead members 61 are used for electrically connecting the circuit substrate 53 and the laminate piezoelectric element 52, retaining members (not shown) are separately required for mechanical connection, thus not only increasing the number of components and the number of operating steps but also complicating the operation of connecting the laminate piezoelectric element 52 and the circuit substrate 53 to each other and increasing the cost. Moreover, the use of the wire members 61 has a further drawback that with increasing nozzle number the space for connection is increased and the size of the head as a whole is increased.
Japanese Patent Disclosure No. 9-286111 shows a prior art entitled xe2x80x9cMethod of Manufacturing Ink Jet Headxe2x80x9d. In this method, piezoelectric elements on an ink head substrate and electrodes on plate-like lead member are bonded together by a conductive adhesive, which is poured via thorough holes formed in the lead member.
In other words, the disclosed prior art features in forming through holes in the substrates. However, from the standpoints of the productivity and cost, the least permissible hole diameter and land diameter of the thorough holes formed in the glass fiber epoxy resin substrate are 0.3 and 0.5 mm, respectively, in the case of the single-layer substrate and 0.3 and 0.7 mm, respectively, in the case of the multiple-layer substrate (the least permissible inter-land distance being 0.2 mm).
This means that the least permissible electrode pitch is 0.7 mm in the case of the single-layer substrate and 0.9 mm in the case of the multiple-layer substrate, that is, it is possible to obtain a resolution only up to 36 dpi per row in the case of the single-layer substrate and up to 28 dpi in the case of the multiple-layer substrate.
Therefore, for obtaining, for instance, an ink jet head capable of printing with an electrode pitch of 600 dpi per pass, at most 17 piezoelectric element rows are necessary in the case of the single-layer substrate, and at most 22 piezoelectric element rows are necessary in the case of the multiple-layer substrate.
With such a system, it is impossible to obtain size reduction of a high resolution ink jet head. Even if such size reduction is possible, it is difficult to realize cost reduction due to part expenditure increases.
The present invention was made in view of the above background, its object is to provide an ink jet head, in which electric bonding members are provided between a piezoelectric element for providing oscillations to a pressure chamber communicated with an ink jet nozzle and a circuit substrate having a head driving circuit, thus permitting improvement of the qualitative reliability and the yield, cost reduction, head size reduction, prevention of erroneous head operation and rupture of a driver IC (i.e., head driving circuit).
According to the present invention, there is provided an ink jet head comprising a piezoelectric element having inner and outer electrodes in electric conduction to one another and for providing vibrations to a pressure chamber communicated with an ink jet nozzle, and a circuit substrate disposed near the piezoelectric element and having a head driving circuit, wherein:
the substrate and the piezoelectric element are connected to each other via electric bonding members interposed between them.
The piezoelectric element is a laminate piezoelectric element and the laminate piezoelectric head is constituted by a plurality of sub-elements. The outer electrodes are formed separately for each sub-element, and extend along side surfaces of the laminate piezoelectric element and the end thereof nearer the circuit substrate.
Thus, the circuit substrate and the piezoelectric element are connected to each other both electrically and mechanically at a time by the electric bonding members provided between them.
The head driving circuit is formed on the circuit substrate on the side thereof opposite the piezoelectric element.
Thus, drive signal from the head driving circuit is provided via the circuit substrate to the piezoelectric element.
In the ink jet head, a reinforcement member is provided between the piezoelectric element and the circuit substrate.
Thus, the mechanical strength of connection of the piezoelectric element and the circuit substrate to each other can be increased by the reinforcement member.
In the ink jet head, the electric bonding members are constituted by bumps and the circuit substrate and the piezoelectric element are connected to each other both electrically and mechanically at a time by the bumps provided between them.
In the ink jet head, wherein the electric bonding members are constituted by an anisotropic conductive film.
Thus, the circuit substrate and the piezoelectric element are connected to each other both electrically and mechanically at a time by the anisotropic conductive film provided between them.
The bump is solder, Au or Cu and the anisotropic conductive film is obtained by dispersedly burying carbon fibers, carbon particles, Au-plated metal particles, conductive rubber particles or fine metal wires in silicone rubber.
According to another aspect of the present invention, there is provided an ink jet head comprising:
a pressure chamber communicated with an ink jet nozzle;
a circuit substrate having a circuit for producing a drive signal;
a piezoelectric element for providing vibrations to the pressure chamber in response to the head driving signal;
bonding members interposed between the circuit substrate and the piezoelectric element for connecting them.
Other objects and features will be clarified from the following description with reference to attached drawings.